1. Field of the Invention
The present invention relates generally to a rack and pinion power steering apparatus for automotive vehicles, and more particularly to a structure for loosely fitting a hydraulic annular piston to the end surface of a rack.
2. Description of the Prior Art
As is well known, power steering apparatuses have widely been incorporated in automotive vehicles for facilitating of vehicle steering. Usually, the power steering apparatus includes a control valve, a power cylinder and an oil pump including discharge and pressure control valves. A rack and pinion power steering apparatus is of one type of power steering apparatuses. In this rack and pinion type, a hydraulic piston connect to a rack for actuating a vehicle steering device is reciprocably moved within a hydraulic cylinder by the aid of hydraulic fluid. By the way, within the above hydraulic cylinder, since the piston must partition the inside space of the cylinder into two hydraulic fluid chambers, it is very important to stably maintain fluidtightness between the outer peripheral surface of the hydraulic piston and the inner peripheral surface of the hydraulic cylinder. For the above-mentioned purpose, there has been proposed a rack and pinion power steering apparatus such that the piston is elastically attached to the end of the rack in order to eliminate a harmful influence upon the fluidtightness due to misalignment between the piston and the rack within the cylinder. In this type of apparatus, however, since the annular piston is fixed to a boss portion formed at the end of the rack by caulking, the caulking work inevitably requires a skill in the assembly process of the piston and the rack.
To eliminate the above-mentioned skill, the same applicant has proposed a rack and pinion power steering apparatus such that the piston is elastically attached to the end of the rack by use of a bolt. In this apparatus, however, there still exists a problem in that: since the piston mounting bolt is screwed into only the boss portion of the rack, a load applied to the piston due to a difference in fluid pressure between two hydraulic chambers within the piston housing is concentratedly transmitted to the base of the small-diameter rack boss portion, thus the boss portion may be broken while the annular piston is slidably moved to and fro within the piston housing.
A more detailed description of the prior-art rack and pinion power steering apparatus will be made with reference to the attached drawings under DETAILED DESCRIPTION ON THE PREFERRED EMBODIMENT.